A waveguide is a structure that guides waves, such as electromagnetic waves or sound waves. There are different types of waveguides for each type of wave.
For optical waves, the corresponding waveguide is an optical waveguide. It is a physical structure that guides electromagnetic waves in the optical spectrum. As examples of optical waveguides, light tubes or light pipes are physical structures used for transporting or distributing natural or artificial light for the purpose of illumination.
In electronic devices, molded plastic light tubes are commonly used in the electronics industry to direct illumination from LEDs (light emitting diode) on a circuit board to indicator symbols or buttons in the front panel. These light tubes typically take on a highly complex shape that either uses gentle curving bends as in an optic fiber or has sharp prismatic folds which reflect off the angled corners. Multiple light tubes are often molded from a single piece of plastic, permitting easy device assembly since the long thin light tubes are all parts of a single rigid component that snaps into place.
Light tube indicators make electronics cheaper to manufacture since the old way would be to mount or install a tiny lamp into a small socket directly behind the spot to be illuminated. This often requires extensive hand-labor for installation and wiring. Light tubes permit all lights to be mounted on a single flat circuit board, but the illumination can be directed up and away from the board by several inches, wherever it is required.
Some products require different color LEDs to be closely placed in certain pattern. Thus different light pipes are required for the light transfer. The ideal solution is that light pipe are isolated from each other and mounted separately to avoid light leakage and interference. But this will cause high product cost and complex production process. A common solution in the industry is to add some rectangle bars with the same material as the light pipe (or called rectangular parallelepiped) as bridge to connect all light pipes for low cost. For cost reason, the rectangular bars and the light pipes are molded together as a single component. However, the connection bridges may cause light leakage and interference between different light pipes to which they connect.